made an adjustable piston for the 880

[Rob M]

well, u have certainly dug yourself a large pile of work! The good news is , when u get it working , 4 pumps will have the swept volume of almost 7 pumps previosly.. So 12 pumps will have the valve maxed out shooting 900fps or so.. lotta work , i commend the effort

[bhh]

Do you think an aluminum pump arm will hold up, or should I make one out of steel?

I wonder how hard it will be to pump at stroke 12?

[avator]

You may want to look into PPE (Personal Protective Equipment) I would thing at least a helmit and athletic cup.... lol

[bhh]

You may want to look into PPE (Personal Protective Equipment) I would thing at least a helmit and athletic cup.... lol

Lol. 

But:

I've expressed that I'm interested in getting about 12 ft lbs and plenty of guys here push their 880s to that level. Rob installed a gauge and pushed it well beyond that point.  I assume he has all his male bits and no head injury. 

And I'm using a steel tube with a .065" wall instead of the stock aluminum with a .035" wall.

Seems like I'm not pushing it too much.

[avator]

I've been following the thread since it began. I think I was the first to get one of Rob's piston heads. I tested them in the older Ted Williams and 881 but the brass tube with the slots in them just kept chewing up the o-rings. I didn't have anything newer at the time except for Betty Lou's Metal/Metal 880 and I feared for my life when I thought about fooling with it. I have a few options now and I may pull them back out for another go round. We use our 880s for accurate plinking at 30 - 35 yds. Rarely do we put more than 6 pumps in them. I do enjoy tinkering though.

[Rob M]

hey bill , hope all is well!@
as far as the pump arm concern , i think aluminum is fine is you can mill one.. I think the pumping effort will be like a 392 on 12 pumps , mine was when i got to the 20s and urs will be there by 12 pumps , or less according to the math..I think any wood or plastic in the pump arm design will be the downfall. ALSO ,any oppportunity to use bigger screws at stripping points or bulging points will make a world of difference.I still have all my body parts, even after installing a gauge and adding tremendous volume to the 880.. Neighbors likely thought it was a 22, i still regret not having a chrony when i started , i was getting the best results when i made the youtube video , and after that when I was getting 910 fps it sounded substantially weaker and the pump tube was already beat to heck.

[Rob M]

were i to start over.. heres a simple list id do , and the price would more than the double the guns cost.. this would be the combo for 1100 fps with a 7.9grain IMO
first , get an old scool metal pump arm for the new gun
Next, id make an adjustable piston with 2 113 orings.smooth it out super nice with 400 grit
Next id order .732 id stainless tube , id then turn it down to fit the frame , and duplicate the tube  , just .500 longer.
Then , id get another 3000 psi gauge off amazon , drill my 11/32 hole in the special spot right behind the abutement where you CANNOT hit anything vital , theres nothing there. This would serve as my gauge and Volume increase.
with these mods, I think 1000 would be super easy , 1100 would be pushing the frame and everything to the brink , and likely ID need to pump well beyond my old 2000psi , probably 2400 but the all metal zero slop pump assembly plus the added strokje length would make it possible;
Some people would say " rob , thats impossible , youre an idiot " .. But these same folks never had one pushing 910 fps and sounding like a 22 rimfire either.

[Rob M]

http://www.ebay.com/itm/DOM-STEEL-TUBING-1-x-134-x-60-ALLOY-1020-1026-/310345332562?hash=item484205f752:g:4S4AAOxyVX1RxIRt

this is the cheapest section of .732 tube i could find, its DOM

even 10 inches from the metal supplier is 40 bux shipped

http://www.onlinemetals.com/merchant.cfm?pid=14868&step=4&showunits=inches&id=902&top_cat=1

[Rob M]

A huge factor would not be human strength , it would always be the rigidity of the pump assembly to allow it to pump beyond 2200 psi.. And anyone looking for power from an 880 , I think thats the number one culprit for losses.

[avator]

All very interesting but I just woke up from working the night shift last night to a box dropped off by UPS containing my most recent purchase. Another unmolested metal/metal 880. Time to go molest it. Just the typical mods for this one:
Remove the flat spring
Polish the trigger contact points and take a bit off of the sear hook to shorten the pull
Open the pellet port on the clams for easier loading of the Winnie Domes.
Fill the stock with silicon caulk
Clean and tape the straw barrel
Glue the BB door closed and JB Weld the BB rabbit hole
Might put that adjustable double o-ring piston pump head in if the tube isn't slotted.
Then we'll see where we are.. If anything is significant I'll begin a thread.
Once again, my goal is not to break any power records. Just an accurate fun shooting plinker without spending more money than the end result is worth.

[bhh]

I made some progress today.

I turned an aluminum sleeve and inserted a section of the original pump tube. I used Loctite 609 and a press fit. I heated the sleeve and tapped the valve tube in place. Then faced it off.  Here are the two parts together:





Then I heated the new steel pump tube and used the same heat/hammer/Loctite 609 method to insert this into the new pump tube.  Here are the three parts together. I don't think I'll get any air leakage.




So now this will fit on the valve assembly and the original tube/sleeve assembly will stop flush with the end of the abutment. The piston face will contact the abutment and tube/sleeve at the same time.

For those concerned with safety, the pressure will be contained by the original tube, an aluminum sleeve press fit over it, and a .065" steel tube press fit over that. I think that will be safe.

[Rob M]

very cool.. i get it now.. so the piston will still run its full length stroke..very cool./ No pressure concerns , the stock compresion tube can handle it and thats basically paper

[bhh]

very cool! Im assuming the pics are the end of the new tube where it adjoins to the valve..

Yep.

And, yes, the piston will run it's full stroke the same as a stock piston.

[Rob M]

u gotta ,make a big ole piston now

[bhh]

u gotta ,make a big ole piston now

Yep. After these interference fits I made today machining a piston sounds easy.

[Rob M]

hahahaahaa, yes,, just make sure the piston connection points are within a good tolerance.this should be pretty cool..

[Rob M]

i actually keep seatching for the .732 id tube on ebay.. I guesss i could always make some with a boring bar and the steady rest

[bhh]

i actually keep seatching for the .732 id tube on ebay.. I guesss i could always make some with a boring bar and the steady rest

I need a better lathe/boring bar set-up before I attempt something like that. I think it would be tough to get the surface finish I need on tube that long.

[Rob M]

Yes, would not be easy,even with aluminum..youd need a way to follow up after the machining to hone the tube.. like a custom made 200 grit sanding bit in the tailstock at high rpm

[Rob M]

actually one way it would be easy is in the spindle bore.. have the work almost level with the chuck ( just enough proud to indicate) run the boring bar in 2.5, flip it , do the same , and your have a mirror finish on aluminum.. Bad news for me is my spindle bore is only .78 , if it were an inch , I could make custom long tubes.